Shadow mask frame construction

ABSTRACT

In a shadow mark for use in a colour television receiving tube of the type comprising a rectangular mask plate, and a rectangular frame member including a rectangular side wall adapted to support the mask plate and a reinforcing flange, the angle between the side wall and the reinforcing flange is made larger than 90* at the corners of the rectangular frame member and to gradually increase toward the longitudinal centres of the shorter sides and the longer sides of the rectangular frame member.

United States Patent Tsuneta et al. 1 51 June 5, 1973 54 SHADOW MASKFRAME 2,897,392 7 1959 Fiore ..313 92 B CONSTRUCTION 3,497,746 2/1970Duistermaat et aL... .313/85 S 3,549,932 12/1970 Lindeman ..313/85 S[75] Inventors: Asahide Tsuneta, Kawasak1; Sh1nlch| 3,581,135 /1971Garren I g v 4 5 Sawagata, Tokyo, both of Japan 3,601,650 8/1971Pappadis ..3l3/85 s [73] Assignee: Tokyo Shibaura Electric Co., Ltd.,

Kawasakbshi, Japan Primary ExaminerRobert Segal AttorneyR. D. Flynn, SH. Frishauf and Leonard [22] Filed: July 27, 1971 Holtz [21] Appl. No.:166,556

[57] ABSTRACT Foreign Application Priority Data In a shadow mark for usein a colour television receiv- Jul 31 1970 h an /7581, ing tube of thetype comprising a rectangular mask i 1970 g t; plate, and a rectangularframe member including a rectangular side wall adapted to support themask 52 US. Cl ..313/ s, 25/25.11 Plate and a'reinfereihg flange, theangle between the [51] InLC] 01 0 0 0 9 02 side wall and the reinforcingflange is made larger 58 Field 01 Search ..313/92 B, 85 s; than at thecorners of the rectangular frame 29/2511 member and to graduallyincrease toward the longitudinal centres of the shorter sides and the.longer sides [56] References Cited of the rectangular frame member.

UNITED STATES PATENTS 8 Claims, 12 Drawing Figures 2,795,718 6/1957 VanKekken et al ..313/85 S PATENIEUJUH 5:975

SHEET 1 BF 2 FIGS SHADOW MASK FRAME CONSTRUCTION This invention relatesto a shadow mask for use in a colour television receiving tube and moreparticularly to an improved construction of the frame for supporting amask plate.

A colour television receiving tube generally comprises an envelopeincluding a funnel having an integral neck, and a face plate joined tothe opening of the funnel. On the inside of the face plate is secured amask plate provided with a plurality of small perforations forcontrolling the passage of electron beams from a source of electronbeams contained in the neck. Usually, the mask plate has a rectangularconfiguration and is provided with a curved surface having at least onecentre of curvature located on the side of the source of the electronbeams. The radius of curvature of the curved surface is the same as thatof the curved inner surface of the face plate which is coated withphospor and it is desired that the distance between the inner surface ofthe face plate and the curved surface of the mask plate should beuniform at all points. Furthermore, as the metal plate constituting themask plate is extremely thin, in order to prevent deformation of themask plate, it is mounted on a rigid rectangular frame member which isremovably mounted on pins secured to the flange of the face plate.

One example of the method of manufacturing the rectangular frame memberis as follows. First, a metal strip having a suitable thickness, 2.6mmfor example, is prepared and the metal strip is bent longitudinally by90 to have a cross-section of a letter L. The L shaped metal strip isthen bent transversely at four spaced apart points into a rectangularconfiguration and the opposite end of the strip is welded together toform a flat rectangular frame member. To securely support the curvedmask plate, the rectangular frame member is then bent by means of apress or the like to have the same curvature as that of the periphery ofthe mask plate. Due to the mechanical working operations describedabove, internal strain is created in the frame member so that it isnecessary to subject the frame member to a suitable heat treatment.However, some strain often remains unremoved.

During the evacuation step of the envelope following the incorporationof the shadow mask assembly comprising the mask platesecured to theframe member into the envelope of the receiving tube, the shadow mask isheated to a temperature of about 450C. Due to the residual strain'notremoved even by this heat treatment the frame member has a tendency totwist about its axis. Such twisting causes the mask plate to deformafter completion of the receiving tube so that the chance of creatingthe so-called misslanding increases in which the electron beams fail tocorrectly irradiate the phosphor dots of red, blue and green, forexample, applied on the inner surface of the face plate, thus causingcolour break-up of the picture image. For this reason, it is highlydesirable to provide an improved rectangular frame member capable ofdecreasing the strain created by the mechanical working operations.

In the colour television receiving tube including a plurality ofphosphor dots formed on the inner surface of the face plate, theso-called black matrix type tube has been developed in which thediameter of the perforations of the mask plate for controlling thepassage of the electron beams is made larger than that of the dots. Forthis purpose, after forming the phosphor dots, the shadow mask isremoved from the face plate and is then dipped in an etching solution toenlarge the diameter of the perforations so as to be larger than that ofthe phosphor dots. The etching solution remaining at the bent portionsand corners of the rectangular frame member after the etching treatmenttends to corrode, oxidize and rust the frame member and fine particlesformed by such chemical reactions tend to close the perforations. Inthis manner, it is desirable to provide an improved rectangular framemember capable of preventing the retention of residual etching solution.

Accordingly, it is an object of this invention to provide an improvedshadow mask for colour television receiving tubes having a rectangularframe member of a configuration capable of giving lesser tendency ofpreserving the strain created by a mechanical working operation andpreventing the etching solution from remaining.

Another object of this invention is to provide a shadow mask including anew and improved rectangular frame member for supporting the mask plate,which is not necessary to be annealed to remove the strain createdtherein by the mechanical working thereof.

SUMMARY OF THE INVENTION These and further objects of the invention canbe ac complished by providing a shadow mask of a colour televisionreceiving tube of the class comprising a rectangular mask plateincluding a curved rectangular face having at least one centre ofcurvature on the side of a source of electron beams contained in theenvelope of the tube, and a peripheral flange surrounding the curvedrectangular face and bent toward the source of electron beams; thecurved rectangular face being provided with a plurality of smallperforations for controlling the passage of the electron beam; and arectangular frame member including a rectangular side wall adapted toreceive the peripheral flange and a reinforcing flange bent inwardly ofthe rectangular frame member away from the side wall, the side wallhaving a curved free edge having the same radius of curvature as theperiphery of the mask plate, characterized in that the angle between theside wall and the reinforcing flange of the rectangular frame member ismade larger than at the corners of the rectangular frame member andgradually increases towards the longitudinal centre of each side of therectangular frame member.

Selection of the angle between the rectangular side wall and thereinforcing flange of the rectangular frame member to be larger than 90not only decreases the strain created therein by the mechanical workingbut also prevents the etching solution utilized to etch the shadow maskfrom remaining on the rectangular frame member. This design furtherincreases the area of the mask plate through which the electron beampasses or the effective area of the mask plate. However, the angleshould be selected to a suitable value not to decrease the mechanicalstrength of the frame member. The angle is decreased gradually from thelongitudinal centre of each side toward the corners of the frame memberfor the purpose of easy working.

Where said angle at the longitudinal centre of the longer side of therectangular frame member is made larger than that at the longitudinalcentre of the shorter side it is possible to work more easily the framemember so as to decrease internal'strain, and where at least oneperforation is provided for the reinforcing flange at each corner of therectangular frame member, the strain due to mechanical working can bereduced further and the etching solution can be more readily drained.The advantageous merit of the frame member can be enhanced by increasingthe width of the side wall at the longitudinal centre of each side thanthat at the corners. Longitudinal grooves having a semicircularcross-section may be provided for the reinforcing flange.

This invention can be more fully understood from the following detaileddescription when taken in connection with the accompanying drawings, inwhich:

FIG. 1 is a side view, partly broken away, of a colour televisionreceiving tube employing a shadow mask embodying the invention;

FIG. 2 is a perspective view, partly broken away, of the shadow maskshown in FIG. 1;

FIG. 3 is a perspective view of the rectangular frame member of theshadow mask shown in FIG. 2;

FIGS. 4, and 6 show coss-sections at a corner, centre of the shorterside and centre of the longer side of the rectangular frame member shownin FIG. 3 taken along lines 4-4, 5-S and 66, respectively;

FIG. '7 is an enlarged perspective view of a corner of the rectangularframe member shown in FIG. 3;

FIG. is a perspective view of a modified rectangular frame member;

FIG. 9 is an enlarged perspective view of a corner of the frame membershown in FIG. 8; and

FIGS. 10, 11 and 12 show cross-sections at a corner, centre of theshorter side and centre of the longer side of the rectangular framemember shown in FIG. 8, taken along lines l010, IIl1 and 12-12,respectively.

The envelope of a colour television receiving tube shown in FIG. 1comprises a funnel 2 having an integral neck which contains a source ofelectron beams I and a face plate 9. The shadow mask 8 embodying theinvention is removably mounted in the peripheral flange 3 of the faceplate by means of pins 7 secured thereto. The outer edge of the flange 3is sealed to the opening of the funnel 2 at 14 by means of a low meltingglass for example. On the inner surface 15 of the face plate 9 areformed, such as by coating, a plurality of phosphor dots, not shown,adapted to emanate red, blue and green colours, for example, whenimpinged upon by the electron beams in a manner well known in the art.The face plate 9 is substantially rectangular and its inner surface 15is a curved surface having at least one centre of curvature located onthe side of the source of electron beams 1.

As shown in FIG. 2, the shadow mask 8 comprises a rectangular mask plate18, and a rectangular frame member 19 supporting the mask plate 18. Themask plate 18 has a curved surface having a plurality of fineperforations 16 for controlling the passage of the electron beamsimpinging upon the phosphor dots and the same radius of curvature as theinner surface 15 of the face plate. The periphery of the mask plate isbent at right angles towards the source of electron beams to form aperipheral flange 17 used to mount the mask plate on the frame member.

The rectangular frame member 19 comprises a vertical side wall 20adapted to receive the peripheral flange 17 of the musk plate 18 and areinforcing flange 22a projecting inwardly from the side wall and isbent at varying angles as will be described later with respect to thevertical side wall 20. The free edge 23 of side wall 20 is curved withthe same radius of curvature as'the periphery of the mask plate 18. Theperipheral flange 17 of the mask plate is fitted on the vertical sidewall 20 and welded thereto as by welding whereby the mask plate issecurely fixed to the rectangular frame member The cross-sectionalconfigurations at a corner, longitudinal centre of a shorter side 24 andat the longitudinal centre of a longer side 25 of the rectangular framemember 19 are shown by FIGS. 4, 5 and 6, respectively. Moreparticularly, the angle between the vertical side wall 20 and thereinforcing flange 22a equals +a,, 90+e and 90+a respectively, at thesesections. The cross-sectional configuration of the reinforcing flange22a is straight at any point of respective sides. Desirably, the abovedescribed angles have a relation a, a a but the angular relation mayalso be a a and a, a Angles a and a gradually decrease from thelongitudinal centres of respective sides toward the corners of therectangular frame member. As shown in FIGS. 4-6, the surface of thereinforcing flange is inclined toward the source of electron beams. Theinclined angle is selectively determined within (1,, a and a The widthsof the vertical side wall 20 at various sections equal 1,, l and 1 asshown in FIGS. 4, 5 and 6 and it is desirable that they satisfy arelation l, l l As shown in FIG. 3, each side wall has a free edge 23and a stationary edge opposite the free edge, the radius of curvature ofthe stationary edge being different from thatof the free edge. Thewidths of the side walls (or the distance) between the free edge and thecorresponding stationary edge are 1 1 and 1 respectively at the corneralong line 4-4, the longitudinal center of the shorter side wall alongline 5-5 and the longitudinal center of the longer side wall along line6-6. However, if desired, the relation may be l, l and l, l The widths land 1 at the longitudinal centres of the shorter and longer sidesgradually decrease toward the corners of the rectangle. In this manner,by making the width of the side wall 20 larger at the centres ofrespective sides than at the corners of the rectangular frame member, itis possible to increase the mechanical strength of the frame member.

By selecting respective angles in ranges 041 5 15, a 10 5 and 15 55,more particularly, a, 5, a l0 and a 30 it is possible to minimize thestrain created by the mechanical working operations of the frame memberas well as the thermal deformation caused by the heat treatment of theframe member. thus effectively preventing decrease in the mechanicalstrength of the frame member.

At four corners of the frame member, since the reinforcing flange 22aand the side wall 20 are bent together at substantially right angles,maximum strains are created at these corners. Accordingly, in order toabsorb or eliminate the strains at the corners, it is advantageous toform at least one perforation 26 through the reinforcing flange 22a ateach corner as shown in FIG. 7. In the case shown therein, there areprovided six such perforations 26.

One method of fabricating the rectangular frame member 19 is as follows.First, a metal strip having a desired thickness, 2.6mm for example,width and 7 points and the opposite ends of the strip are weldedtogether to obtain a rectangular frame member. The frame member is thendeformed by means of a press such that its free edge (the upper edge asviewed in FIG. 3) will have the same curvature as the periphery as themask plate 18. Then, if desired,'the frame member may be subjected to aheat treatment to remove the strain caused by the working operations.Thereafter, the mask plate 18 is mounted on the rectangular framemember. Fixtures provided on respective sides of the frame member forreceiving the pins shown in FIG. 1 are not shown.

A modified rectangular frame member 27 shown in FIGS. 8 to 12 alsocomprises a vertical side wall 20 and a reinforcing flange 22b, and thefree edge 23 (upper edge as viewed in FIG. 8) of the vertical side wall20 is curved with the same radius of curvature as the periphery of themask plate in the same manner as, in the first embodiment. However, thecross-sections at the corner, at the longitudinal centre of the shorterside 24 and at the longitudinal centre of the longer side 25 taken alonglines l10, 11-11 and 12-12 in FIG. 8 have configurations as shown inFIGS. 10, 11 and 12, respectively. More particularly, the reinforcingflange 22b is not bent sharply at right angles with respect to thevertical side wall 20 but instead flange 22b and side wall 20 areinterconnected by a rounded connection of a radius of curvature R whichis selected to be equal to one to three times the thickness of the metalstrip constituting the frame member. The inner edge of the flange 22b iscurved in the opposite direction with a radius of curvature of R Theangle between a tangent line 28 to the inner curved edge of flange 22band the inner side of the vertical side wall 20 equals 90+a at thecorner, 90"+ct at the longitudinal centre of the shorter side 24 and90+oz at the longitudinal centre of the longer side 25 of therectangular frame member. As above described, these angles have arelationa (1 04 Where these angles are selected within ranges a 7, 01 430 and a 45 it is pos sible to minimize the strain in the frame memberand prevent decrease in the mechanical strength thereof. Angles a and a;decrease gradually toward the corners from their maximum values at thecentre of the sides as in the first embodiment. As shown in FIG. 9, agroove 29 is formed in each side of the reinforcing flange 22b. Eachgroove 29 extends in the direction of each side of the rectangular framemember and the depth of the groove 29 decreases gradually from thecentre toward the corners of the rectangular frame member. The grooves29 form curved surfaces having radius of curvature R as shown in FIGS.10, 11 and 12. The crosssectional configuration of respective grooves issemicircular and their radius of curvature R is substantially equal to15R,. Thus, the depth and width of each groove are the maximum at thecentre of each side of the frame member and gradually decrease towardthe corner. Considering a shorter side 24, for example, the width of thegroove equals l3 to 15mm, the depth about 2 mm, whereas at the centre ofthe longer side 25, the depth of groove equals about 3mm. Although thestrain in the frame member produced therein by the working operationsreduces with the radius of curvature R the mechanical strength of theframe member is also reduced so that it is necessary to select R to aproper value.

In the embodiment shown in FIGS. 10, 11 and 12 the width of the verticalside wall 20 is selected to satisfy a relation l l l in order to preventdecrease in the mechanical strength of the frame member. Similar to theembodiment shown in FIG. 3, the widths l and 1 decrease toward thecorners. However, these widths may be selected to satisfy the conditionsl l and l, I

Again, it is advantageous to form at least one perforation 26 at eachcorner to decrease strain and to provide good drainage of the etchingsolution used to etch the mask plate.

The steps of manufacturing the modified frame member are substantiallyidentical to those described in connection with the first embodimentexcept that grooves 29 and perforations 26 are formed before the metalstrip is bent into the L shaped cross-section.

In the frame member of the shadow mask, since the angle between thevertical side wall and the reinforcing flange is made larger than thetendency of the width of the reinforcing flange for obstructing thepassage of the electron beams is decreased. In other words, it ispossible to increase the effective area of the mask plate in whichperforations 16 are provided. Further more, according to this inventionit is possible to decrease the residual strain. The construction of theframe member is suitable for the black matrix type shadow mask in whichthe diameter of the perforations 16 is enlarged by dipping the shadowmask in an etching solution. Where the reinforcing flange 22b isconstructed to have two oppositely curved surfaces of radii ofcurvatures R and R as shown in FIG. 8, the advantageous effect describedabove can be enhanced. Perforations 26 at the corners not only decreasesthe residual strain but also improves drainage of the residual etchingsolution. Further, the fact that the angle between the vertical sidewall and reinforcing flange of the rectangular frame member increasestoward the corner also contributes to the decrease of the residualstrain.

What we claim is:

1. A shadow mask of a color television receiving tube of the classcomprisingi a rectangular mask plate including' a curved rectangularface having at least one centre of curvature on the-side of a source ofelectron beams contained in the envelope of said tube, and a pcripheralflange surrounding said curved rectangular face and bent toward saidsource of electron beams, said curved rectangular face being providedwith a plurality of small perforations therein for controlling thepassage of said electron beams; and a rectangular frame member havingtwo shorter side walls and two longer side walls adapted to receive saidperipheral flange inclined toward said source of electron beams and areinforcing flange bent inwardly of said rectangular frame and away fromsaid side walls, each of said side walls having a curved free edge and astationary edge opposite said curved free edge, said curved free edgehaving the same radius of curvature as the periphery of said mask plate,

the radius of curvature of said stationary edge opposite to said freeedge of each side wall differing from that of said free edge, the anglebetween said side wall and said reinforcing flange equaling 90+a 90+orand 9O+a at the corner, at the longitudinal centre of said shorter sidewall and at the longitudinal centre of the longer side wall,respectively, and said angles 04,, a and a having a relation a a theangles and a gradually decreasing from the longitudinal centres of saidshorter and longer side walls toward the corner of said rectangularframe member wherein a =5 to l5,-a =l0 to 45, and a =l5 to 55.

2. The shadow mask according to claim 1 wherein said side walls havewidths l l and I at the corners, at the longitudinal centre of theshorter side and at the longitudinal centre of the longer side,respectively, of said rectangular frame member, said widths beingmeasured between said stationary and free edges of said side walls andhaving a relation l l l and said widths l and I gradually decreasingfrom said centres toward said corners.

3. The shadow mask according to claim 1 wherein said reinforcing flangeis formed with at least one perforation at each corner of saidrectangular frame member.

4. The shadow mask according to claim 1 wherein the transversecross-section of said reinforcing flange of said rectangular framemember is substantially linear at any side thereof.

5. The shadow mask according to claim 1 wherein said reinforcing flangeat each side of said rectangular frame member is provided with a grooveextending in the longitudinal direction of said side, the depth andwidth of said groove gradually decreasing from the centre of said sidetoward the corners of said rectangular frame member, and said groovebeing convexed toward the free edge of said side wall.

6. The shadow mask according to claim 5 wherein said side walls havewidths l l and 1 at the corners, at the longitudinal centre of the theshorter side and at the longitudinal centre of the longer side,respectively, of said rectangular frame member, said widths beingmeasured between said stationary and free edges of said side walls andhaving a relation l, l l and .said

widths l and I gradually decreasing from said centres toward saidcorners.

7. The shadow mask accordingto claim 5 wherein said reinforcing memberis provided with at least one perforation at each corner of saidrectangular frame member.

8. The shadow mask according to claim 6 wherein said reinforcing memberis provided with at least one perforation at each corner of saidrectangular frame member. a, a a the angles a and a gradually decreasingfrom the longitudinal centres of said shorter and longer side wallstoward the corner of said rectanular frame member, wherein (1 5 to 15,0: 32 10 to 45,

1. A shadow mask of a color television receiving tube of the classcomprising: a rectangular mask plate including a curved rectangular facehaving at least one centre of curvature on the side of a source ofelectron beams contained in the envelope of said tube, and a peripheralflange surrounding said curved rectangular face and bent toward saidsource of electron beams, said curved rectangular face being providedwith a plurality of small perforations therein for controlling thepassage of said electron beams; and a rectangular frame member havingtwo shorter side walls and two longer side walls adapted to receive saidperipheral flange inclined toward said source of electron beams and areinforcing flange bent inwardly of said rectangular frame and away fromsaid side walls, each of said side walls having a curved free edge and astationary edge opposite said curved free edge, said curved free edgehaving the same radius of curvature as the periphery of said mask plate,the radius of curvature of said stationary edge opposite to said freeedge of each side wall differing from that of said free edge, the anglebetween said side wall and said reinforcing flange equaling 90*+ Alpha1, 90*+ Alpha 2 and 90*+ Alpha 3 at the corner, at the longitudinalcentre of said shorter side wall and at the longitudinal centre of thelonger side wall, respectively, and said angles Alpha 1, Alpha 2 andAlpha 3 having a relation Alpha 1< Alpha 2<3, the angles Alpha 2 andAlpha 3 gradually decreasing from the longitudinal centres of saidshorter and longer side walls toward the corner of said rectangularframe member wherein Alpha 1 5 to 15*, Alpha 2 10 to 45*, and Alpha 3 15to 55*.
 2. The shadow mask according to claim 1 wherein said side wallshave widths l1, l2 and l3 at the corners, at the longitudinal centre oftHe shorter side and at the longitudinal centre of the longer side,respectively, of said rectangular frame member, said widths beingmeasured between said stationary and free edges of said side walls andhaving a relation l1< l2< l3, and said widths l2 and l3 graduallydecreasing from said centres toward said corners.
 3. The shadow maskaccording to claim 1 wherein said reinforcing flange is formed with atleast one perforation at each corner of said rectangular frame member.4. The shadow mask according to claim 1 wherein the transversecross-section of said reinforcing flange of said rectangular framemember is substantially linear at any side thereof.
 5. The shadow maskaccording to claim 1 wherein said reinforcing flange at each side ofsaid rectangular frame member is provided with a groove extending in thelongitudinal direction of said side, the depth and width of said groovegradually decreasing from the centre of said side toward the corners ofsaid rectangular frame member, and said groove being convexed toward thefree edge of said side wall.
 6. The shadow mask according to claim 5wherein said side walls have widths l1, l2 and l3 at the corners, at thelongitudinal centre of the the shorter side and at the longitudinalcentre of the longer side, respectively, of said rectangular framemember, said widths being measured between said stationary and freeedges of said side walls and having a relation l1<l2<l3, and said widthsl2 and l3 gradually decreasing from said centres toward said corners. 7.The shadow mask according to claim 5 wherein said reinforcing member isprovided with at least one perforation at each corner of saidrectangular frame member.
 8. The shadow mask according to claim 6wherein said reinforcing member is provided with at least oneperforation at each corner of said rectangular frame member. Alpha 1<Alpha 2< Alpha 3, the angles Alpha 2 and Alpha 3 gradually decreasingfrom the longitudinal centres of said shorter and longer side wallstoward the corner of said rectanular frame member, wherein Alpha 1 5 to15*, Alpha 232 10 to 45*, and Alpha 3to 55*.